1. Field of the Invention
This invention relates to a process for polymerizing or co-polymerizing propylene in the presence of a novel catalyst system.
2. Description of the Prior Art
It is well known that catalyst systems obtained from halide compounds of transition metals (generally titanium trichloride) and organometallic compounds (generally organoaluminum compounds) are suitable as polymerization catalysts for preparing polymers of olefins (especially propylene). Polymers prepared with such catalysts, however, do not have entirely satisfactory stereoregularity. Hence, the resulting polymers have relatively high amorphous contents, and their mechanical properties are inferior. Therefore, a step of removing the amorphous portion is required after polymerization, and in this case the degree of effective utilization of the starting olefins is reduced. Furthermore, these catalysts have low polymerization activities, and the polymers obtained with the catalyst contain so much catalyst residue that, it is necessary to remove it from the resulting polymer.
Many suggestions have therefore been made for catalysts which can afford highly stereoregular polymers. One of the coinventors of the present invention already suggested a catalyst system prepared from titanium trichloride or an eutectic mixture of it with aluminum chloride treated by contact with an acyl halide, and an organoaluminum compound (Japanese Laid-Open Patent Publication No. 26487/72). This catalyst system has greatly improved polymerization activity and stereospecificity, but the activity is still not sufficient as to permit the omission of a step of removing the catalyst residue from the polymer.
On the other hand, various methods have been suggested for supporting a transition metal compound (mainly a titanium compound) on halide compound of a divalent metal, Mg and Mn, (to be referred to as `MX.sub.2 `). In recent years, it has been suggested to perform this supporting by first treating MX.sub.2 with an electron donor compound (e.g., by copulverization) and then treating it with a transition metal compound (with or without another electron donor compound), or by simultaneously treating MX.sub.2, a transition metal compound and an electron donor compound.
Typical examples of these methods include:
(A) a method which comprises pre-treating MX.sub.2 with an organic acid ester and a halogenated silicate were a polysiloxane, and then with a transition metal compound and an organic acid ester (Japanese Laid-Open Patent Publication Nos. 108385/75, 20297/76, 28189/76, 92885/76, and 24293/77),
(B) a method which comprises pre-treating MX.sub.2 with a ketone, an aldehyde, an alcohol or the like, and then reacting the product with a titanium compound (Japanese Laid-Open Patent Publications Nos. 90687/74, 119980/74, and 8238/76),
(C) a method which comprises reacting an organo magnesium compound with an Si-containing compound, and then treating the pre-treated product with a transition metal compound (Japanese Laid-Open Patent Publication No. 133489/74),
(D) a method which comprises pre-treating MX.sub.2 with an electron donor compound and then treating with a transition metal compound (with or without an Si or Sn halide compound) (Japanese Laid-Open Patent Publications Nos. 88983/74, 51378/74, 72383/74, 21989/75, and 13492/77),
(E) a method which comprises copulverizing MX.sub.2, a transition metal compound and a silicon-containing organic compound (Japanese Laid-Open Patent Publications Nos. 86482/74, 55385/76, 55386/76, 55387/76, and 28889/76),
(F) a method which comprises copulverizing MX.sub.2, a transition metal compound and an alcohol, ester, ketone, aldehyde or the like (Japanese Laid-Open Patent Publication No. 55388/76),
(G) a method which comprises preparing a catalyst made from MX.sub.2 and a transition metal compound which has a surface of more than 3 m.sup.2 /g or whose X-ray diffraction spectrum is broader than that of non-activated MX.sub.2 and a transition metal compound (Japanese laid-open patent publication) Nos. 9342/72 and 16986-8/73), and
(H) a method which comprises supporting a titanium compound on MX.sub.2 pretreated with an electron donor compound, and then treating the product with an organic acid ester (Japanese Laid-Open Patent Publication No. 57789/76).
The catalyst systems obtained in these known methods are mainly a combination of an organo aluminum compound (with or without an electron donor compound) and a complex compound in which either a magnesium compound or a titanium compound is treated with an electron donor compound. But, any of these catalyst systems (particularly, in polymerization of propylene) are quite unsatisfactory in crystallinity of polymer. That is, the crystallinity (H.R.) as seen in the examples of these prior arts is in the range of 87 to 93% in terms of H.R. value taking into consideration the amount of non-crystalline polymers dissolved in the polymerization solvent. Further, in the prior art, hydrogen (as a chain transfer agent) is not used in the polymerization. When it is used in order to obtain a polymer which has a practical M.F.I. value (i.e., 1 to 20 g/10 min.), the H.R. value is reduced by 2 to 5%. Thus, when polypropylene is produced by the catalyst as proposed above, and non-crystalline polymers are not removed at all their practical mechanical properties of the resulting polymer are quite unsatisfactory.
In addition, these known methods do not at all suggest a method as in the present invention in which a mixture or a reaction product of a titanium compound and an electron donor compound is supported on a magnesium dihalide compound copulverized with an acyl halide, and the resultant is then activated with an organoaluminum compound an electron donor compound. It is an unexpected and excellent effect that in the practical MFI range, the H.R. value of the polymer produced with the thus obtained catalyst exhibits 94 to 98%. It is therefore not too much to say that the production of polypropylene having the same practical properties as in commercially available polypropylene has first become possible by the process of the present invention without removing its catalyst residue and amorphous portion.
It is believed that a catalyst system prepared from a solid component resulting from the supporting of a titanium compound on a magnesium halide and an organoaluminum compound (to be referred to as "catalyst system A") has higher polymerization activity than the conventional catalyst systems, and can possibly omit a process to remove the catalyst residue from the resulting polymer. However, the resulting polymer has a relatively low crystallinity, and without removing an amorphous polymer, it does not exhibit satisfactory properties in practical use. Furthermore, since the polymerization activity of this catalyst system per unit amount of the carrier is not high enough, a relatively large quantity of the magnesium dihalide remains in the resulting polymer, and will cause the coloration of the product or the corrosion of the polymerization apparatus. Much difficulty is encountered in the production of polymers, too, because the powdery polymer has a low bulk density.
On the other hand, a catalyst system prepared from a solid component resulting from the supporting of a titanium tetrahalide on a carrier obtained by pre-treating a magnesium dihalide with both an organic acid ester and a silicon compound, and an organoaluminum compound (to be referred to as "catalyst system B") exhibits a high stereospecificity when it is used to produce polymers having a low melt flow index. However, when polymers having a practical melt flow index are produced with this catalyst system B with control of molecular weight, they have greatly reduced stereoregularity. Unless an amorphous polymer is removed, the obtained polymers do not have feasible mechanical properties. The catalyst system B is therefore not yet satisfactory for basically simplifying the manufacturing process and reducing the cost of production.
The widely available conventional PP has a stiffness of higher than 11,000 Kg/cm.sup.2 at a melt flow index ("MFI" or "M.F.I." for short) of 3 g/10 min. The above stiffness value corresponds to the H.R. of about 94%, which is critical value of practical use.
The PP having lower H.R. than 94% cannot exhibit good mechanical properties and must be treated with a suitable solvent to remove its amorphous portion for practical use.